"Exploration of Oxide Surfaces for Environmental Pollution Reduction"

Anthropogenic emission of Nitrous oxide (NOx) in the atmosphere is harmful to human beings as well as to the environment by causing air pollution, acid rain, and greenhouse effect. Reducing the polluting NOx contents into harmless N2 and O2 gases has been of immense research interest recently. One of the most promising approaches is the photocatalytic reduction. Surfaces made of transition-metal oxides such as TiO2, SnO2 and ZnO etc are able to carry out these photocatalytic redox reactions by incidence of solar

Among them TiO2 is considered as the most promising semiconductor photocatalyst due to its high stability, non-toxicity and cost-effectiveness and has enormous applications in many fields like renewable energy, environmental protection, industries etc. TiO2 surfaces are also helpful in the photocatalytic reduction of NOx gas molecules. However, pure TiO2 has a wide bandgap (> 3eV) which makes it active in the UV-region of solar spectrum, whereas solar irradiance is maximum in the visible region (1.6 to 3.2 eV).

Therefore, to reduce the band-gap of TiO2 and make it more photocatalytically active in the visible region of solar spectrum, we have been engineering its band-gap by using Density functional theory. We have analyzed the effects of transition-metal dopants on the band-gap of TiO2, and shown that Nb and W doping can make TiO2 a active photocatalyst in the visible-light.

The Scanning Tunneling Microscope (STM) usually provides illustrations of the surface morphology, surface defects and conformation of molecules and is a great tool in characterizing the surfaces of materials. Using DFT we have been simulating the STM images of the pure and NOx adsorbed TiO2 surfaces under various configurations and conformations of the adsorbent molecules. Our work throws more light on the bonding nature of the TiO2 surface, best suitable NOx conformation for more adsorption, and interaction mechanism between the TiO2 surface and the adsorbents

We have been also modelling heterostructures of various transition-metal oxides, so that we can identify a new photacatalyst with enhanced capacity for NOx abatement. In addition, clusters of metal-oxides are modelled on top of TiO2 surface for seeking better photocatalysts.